This invention relates to a method and apparatus for estimating the location of an electronic device based on observations of wireless signals detectable by the device in its vicinity, and the identity of the transmitter(s) of those signals.
It has previously been proposed to provide a location beacon database to function as a positioning system. If the beacons are WiFi (WLAN) access points (APs), such a database contains their MAC addresses, known or estimated positions of the APs, and possibly their power profiles—that is, what signal strength can be expected at various locations around the AP. The database is usually populated by carrying out so-called “war-drives”, gathering at known locations the identities of APs sighted and measurements of the AP signal strengths, and possibly other signal data (e.g. Doppler, error rate). The locations at which the APs are detected may be determined by a Global Positioning System (GPS) receiver.
Because of the burden of carrying out a “war-drive” exhaustively traversing an area of interest, it is usual for the responsibility for building the database to be shared among contributors, who are typically private individual hobbyists. In these circumstances, there is a heavy bias in the data sample towards the routes and locations most often frequented. This so called “arterial bias”, introduces systematic inaccuracies into the deduced AP locations.
The database is used when a user requires a position fix. The process of finding a fix is typically as follows, according to the prior art:    (i) scan for observable APs, with their signal strengths and other signal data;    (ii) look up reference data about the location and possibly power profile of these APs in the database; and    (iii) derive the estimated user position.
However, this approach requires a large amount of data analysis. Sufficient sample data must be gathered to enable the location of each AP to be estimated or inferred, before it can be used to assist in determining location. Consequently, small sets of data relating to the detection of AP signals cannot reliably be used.